An apparatus for performing a treatment with a treatment liquid on a web being continuously fed includes a plurality of plating tanks each holding a plating liquid as the treatment liquid, through which a plastic film is allowed to sequentially pass, so that the desired plating treatment is performed on the surface of the plastic film being continuously fed. In such a web treatment apparatus, for example, slit-shaped inlet and outlet for the feed of the web are provided in each plating tank. In general, such a web treatment apparatus is provided with a liquid seal to prevent leakage of a large amount of the plating liquid from the tank to the outside.
FIG. 1 shows an example of such an apparatus in which copper (Cu) plating is performed on a plastic film (such as a polyimide film, hereinafter, plastic film is simply referred to as “film”) as a base material. FIG. 1 is a plan view schematically showing the general structure of a film treatment apparatus. A film 1 being fed from an unwinding unit 2 in the film feed direction is energized by a power supply unit 3 (energizing step) and then subjected to a plating treatment in a plating unit 5 having a plating tank 4 (plating step). The energizing step and the plating step are sequentially repeated twice or more, so that a plating layer with a desired thickness is formed. After a desired plating layer is formed, the film is taken up by a take-up unit 6. For example, as shown in FIG. 2, the power supply unit 3 includes a feed roll 11 (for example, with a stainless steel (SUS) surface), another feed roll 12 (for example, with a stainless steel surface), and a power supply roll 13 (for example, with a cupper surface) that are placed between the feed rolls 11 and 12 so as to press the film 1 and energize the surface 10 of the film 1 to be plated. As shown in FIG. 3, for example, the plating unit 5 includes a plating tank 4 holding a plating liquid 14 (such as a copper sulfate solution) and copper blocks 15, through which the film 1 is allowed to continuously pass. In general, liquid sealing mechanisms are provided at the inlet and outlet of the plating tank 4 in order to control the amount of leakage of the plating liquid 14 from the plating tank 4 to the outside. It is known that as shown in FIG. 3, a pair of liquid sealing rolls 7 is used in the liquid sealing mechanism (see for example Patent Literature 1). In the film treatment apparatus shown in FIG. 1, the film 1 is fed from the unwinding unit 2 to the take-up unit 6, while the direction of its width is substantially oriented and held in the vertical direction so that good handleability and plating uniformity can be ensured (hereinafter, such feeding of the film with its width direction held in a substantially vertical direction is referred to as “vertically-oriented feed”).
Conventionally, a mechanism as shown in FIG. 4, which is disclosed in Patent Literature 1, is used to ensure the liquid sealing capability at the inlet and outlet of a plating tank 4 as the treatment tank. Specifically, at the inlet and/or outlet of a plating tank 4 filled with a plating liquid 14, a small chamber 31 is formed along the inner wall surface of the plating tank 4 or outside the inlet and/or outlet as shown in FIG. 4, and two (a pair of) spongy-surface rolls 21 are provided inside the outer wall surface 25 of the small chamber 31. The film 1 being fed is nipped between the two spongy rolls 21, and the spongy rolls 21 are placed adjacent to the wall surface A (25) so that the liquid can be sealed therein (a relatively large gap is formed between the roll and the wall surface B (26)). In this case, the clearance between the rolls 21 is fixed. In FIG. 4, the wall surfaces A and B correspond to the surfaces from which the leader lines are drawn. In this method, however, foreign matter may be caught between the web and the liquid sealing roll to form scratches or dents on the surface of the web or to produce wrinkles, uneven tension or other problems.
In order to avoid such problems, there is proposed a method of controlling liquid leakage in non-contact with a web. Patent Literature 2 discloses a method in which the distance between a pair of liquid sealing rolls is made larger than the thickness of a web so that liquid leakage can be controlled in a non-contact manner. This method makes it possible to solve various problems caused by the contact of the liquid sealing roll. In this method, however, when the distance between the rolls is made large, due to the large amount of leakage the capacity of the system for circulating the treatment liquid needs to be increased to an unnecessarily high level. In addition, when the web to be treated is a flexible web such as a resin film, a relatively large amount of the liquid leaks, which causes the problem of fluttering of the web. If the fluttering is severe, the web may come into contact with the roll so that the web surface may be scratched. On the other hand, the distance between the rolls may be reduced so that the leakage amount can be reduced. In this case, however, the space between the roll and the web may be so narrow that the web may come into contact with the roll and be scratched, even when the feed of the web is slightly disturbed. This tendency becomes more remarkable as the web becomes more flexible.
Patent Literature 3 also discloses a technique to control liquid leakage in a similar non-contact manner. The method disclosed in Patent Literature 3 includes providing a plate for preventing leakage of a plating liquid, in which the plate has a rectangular slit which is placed at the opening of a plating tank so that the plate can be prevented from coming into contact with a web (steel tape) and through which the steel tape is allowed to pass (the plate is provided in a direction perpendicular to the steel tape feed direction). It is disclosed that the gap of the slit of the plating liquid leakage-preventing plate is determined taking into account the maximum thickness of the steel tape to be plated and a margin that makes it possible to feed the steel tape without any contact with the slit portion even when the steel tape flutters or becomes defective in shape during the feeding. In other words, this technical idea is to determine the gap of the slit depending on fluttering or defective shape of the steel tape being fed but not to use the gap of the slit to reduce fluttering or the like of the steel tape being fed. Patent Literature 3 also discloses examples in which the thickness of the plating liquid leakage-preventing plate (the length of the steel tape in the steel tape feed direction) is 10 mm or 8 mm, when it is made of a synthetic resin or a metal plate, respectively. As described in the examples, the plating liquid leakage-preventing plate has a dimension of 2,200 mm (length)×400 mm (width), and therefore, it is long and slim. Therefore, it is considered that the thickness of the plate is changed depending on the material it is made of so that the desired stiffness can be imparted to the plate. However, such a technique has the same problem as the technique disclosed in Patent Literature 2, in which when the slit gap of the plating liquid leakage-preventing plate is wide, the amount of leakage becomes large, and when the gap is narrow, the web comes into contact with the plating liquid leakage-preventing plate so that it is scratched. Therefore, it is very difficult to apply the technique to an apparatus for treating a flexible web.
Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No. 2003-147582
Patent Literature 2: JP-A No. 09-263980
Patent Literature 3: JP-A No. 11-256393